I take off all pipes from the tap and to waste, drain them completely and store them. Outside tap is insulated. When I come home I hook it up, an hour or two later my van is filled (by my in van ro) and I disconnect them again etc. If water is flowing it's a lot harder to freeze up. Most times I come home round 4 in winter and it's round about freezing temp and it's been fine.
Thermostat fan heater in van. Extra insulation around membrane incase something would go wrong with heater.